Oxide semiconductor films comprised of some metallic composite oxides have high mobility property and good optical transparency for visible light. Therefore, the films are used for variety of applications such as switching elements or drive circuit elements for a liquid crystal display device, a thin film electroluminescence display device, an electrophoresis method display device, and a powder transfer method display device. Especially, oxide semiconductor films comprising indium oxide/zinc oxide are brought to attention in light of their ease of manufacture, price, or outstanding properties. Specifically, oxides comprising indium oxide/gallium oxide/zinc oxide, or oxide semiconductor films comprising those oxides as a major component have a benefit concerning mobility property which is higher than that of amorphous silicon films. Such oxide semiconductors are usually produced by a sputtering method using a sputtering target composed of each oxide such as indium oxide/gallium oxide/zinc oxide (Patent Documents 1 and 2).
Patent Document 4 discloses a compound of InGaO3(ZnO)m and a method for producing the compound, and the presence of the compound is confirmed. However, there is no disclosure about bulk resistance value, and there is a problem to use the compound for a sputtering target (Patent Document 4). In addition, as for a target comprising one homologous structure, a target comprising InGaO3(ZnO) (see Patent Document 2 and [0091] of Patent Document 1) and a target comprising In2Ga2O6(ZnO) (see [0087] of Patent Document 1) are known, but there is no discussion about a target comprising two or more homologous structures or an effect thereof.
Furthermore, for example, a sputtering target comprised of indium oxide/gallium oxide/zinc oxide using the compound of InGaO3(ZnO)m (an oxide sintered body showing a crystalline structure of homologous phase) causes an abnormal electrical discharge by anomalous growth of the compound shown by InGaO3(ZnO)m during sputtering, and thus there was a problem about defects on the obtained film (see Patent Document 2). In addition, as for a sputtering target composed of indium oxide/gallium oxide/zinc oxide, a target comprising a compound containing an zinc oxide of AXBYO(KaX+KbY)/2(ZnO)m (1<m, X≦m, 0<Y≦0.9, X+Y=2) as a major component is known (see Patent Document 3). However, this sputtering target has problems, for example, the target tends to cause defective appearance such as concavity and convexity found on a surface of the target so-called White-spot; sputtering rate becomes slow; dusts (or particles) of a sputtering material are generated at the sputtering; arc discharge is emitted (arcing), many nodules (agglomerates found on a surface of the sputtering target) are created; there are many differences in quality such as relative density or bulk resistance; and it is difficult to form a large-area film uniformly.
Additionally, a sputtering target composed of an oxide sintered body comprising two or more homologous crystal structures was not known.    Patent Document 1: JP Patent Application Publication No. H08-245220    Patent Document 2: JP Patent Application Publication No. 2007-73312    Patent Document 3: JP Patent Application Publication No. 2007-210823    Patent Document 4: JP Patent Application Publication No. S63-210022    Non-patent Document 1: K. Kato, I. Kawada, N. Kimizuka and T. Katsura, Z. Kristallogr, vol. 143, p. 278, (1976)    Non-patent Document 2: N. Kimizuka, T. Mohri. Y. Matsui and K. Shiratori, J. Solid State Chem., vol. 74, p. 98, (1988)